The present invention relates to a device for the electric measurement of the level of a liquid in a container, particularly in the gas tank of a vehicle, having a conductor foil enclosed by a protective tube, the conductors of which foil form a temperature-dependent, externally heated resistor or electrodes of a measurement capacitor, and having a conductor-foil support which is developed as a protective tube, is swingable at the top and is provided with a spring which presses the support against a bottom of the container.
In one such known device (Federal Republic of Germany OS No. 29 08 449), a support element having a main body and a hinged lid which can be held in position by detent means is provided specifically to receive the conductor foil, which is developed as a ribbon cable. Between the lid and the main body there is a hollow space to receive a section of the ribbon cable and at least one opening for the admission of the fluid to be measured. Parallel to this hollow space an intake duct can also be arranged in the main body, within which duct a bent lower section of the ribbon cable having compensation electrodes is introduced. The upper section of the ribbon cable in this case has the measurement electrodes. The ribbon cable can be placed in the open support element and be held or clamped fast by closing and engaging the lid in the support element. The support element and the lid can be developed as a single piece of plastic, the lid being connected to the main body by at least one film hinge. For easy mounting of the device the support element is swingable on top and provided with a spring which presses the support element against the bottom of the container which receives the fluid. The swingability is obtained in this case in particular by a length of hose fastened on top to the support element. By this swingable development the support element can, it is true, be mounted in containers of different height since the support element adapts itself by variable inclination to the inside height available. However, there is the disadvantage that the place of attachment of the support element must always be located at the highest point of the container since otherwise--if it is fastened at a lower point--the level in the part of the container lying above same cannot be measured. As a result, the possibilities for the use of this measurement detector are limited.
In another embodiment of the device it is also known to develop the conductor having the measurement electrodes and compensation electrodes in the form of a round cable of plastic which is arranged in the container without support element. The cable has concentric annular arrangements of electrodes spaced from each other as conduction paths between which hollow chambers are developed. These round cables can adapt themselves flexibly to different shapes of container but they also do not extend directly from a lower point of attachment to a higher top of the container. Furthermore, the precision of the measurement may be impaired by uncontrolled bendings of the cable. This disadvantage also occurs as a result of the fact that the lower end of the cable is freely movable, unless other measures are taken, and may assume, particularly in a vehicle, positions which are difficult to control and define within the container.
The present invention therefore has the object of developing a device for the electrical measurement of level which has a substantially rigid support as protective tube for a conductor foil of the type mentioned above in such a way that the device can be readily adapted to different shapes of container and can be used, in particular, in cases where the point of attachment of the support to the container is lower than a part of the top of the container. Nevertheless, accurate measurement is possible with this device and, in particular, the level between the point of attachment of the support and the highest portion of the top of the container is included in the measurement.